FAB to cowl seal

jimgreen · #1 01-14-2010, 04:13 PM

I've researched the threads to get guidance on how tight/loose to make the seal on the FAB inlet, but can't find an answer to this:
My first attempt seal has turned out fairly loose.Not exactly a seal.
But perhaps that is how it is meant to be. My FAB is cut 1/4" from the cowl.
I know the engine can move a fair amount, so how loose should the seal be?

jsharkey · #2 01-14-2010, 04:27 PM

Quote:

Originally Posted by jimgreen

I've researched the threads to get guidance on how tight/loose to make the seal on the FAB inlet, but can't find an answer to this:
My first attempt seal has turned out fairly loose.Not exactly a seal.
But perhaps that is how it is meant to be. My FAB is cut 1/4" from the cowl.
I know the engine can move a fair amount, so how loose should the seal be?

I haven't fitted one yet and everything works well. Perhaps I'll gain a fraction of a knot when I do fit it but it makes it easier for now during Phase 1 to take the cowl on and off. Oh and I haven't fitted the air ramp baffle seals to the air inlets yet either and cooling is fine too.

Jim Sharkey RV-6

JordanGrant · #3 01-15-2010, 07:27 AM

Definitely read the following thread. We've been discussing this issue a bit lately.

http://www.vansairforce.com/communit...ht=FAB+failure

caryr · #4 01-15-2010, 07:37 AM

there should be an interferrence fit with the lip of the intake flange on the cowl.

After putting on the cowl you should have to stick your hand partially into the intake flange and smooth out the rubber flashing around the FAB inlet. Or a better term might be ' push it into place'.

So Interference with the flange lip , but clear of the cowl fiberglass.

JonJay · #5 01-15-2010, 08:17 AM

I believe the plans or instructions call for something like 3/4"?
The engine will move a lot on start up and shut down. You do not want to risk the FAB hiting the cowling. At 1/4" you will also have a very difficult time getting the cowl in place.
There should be a reasonable seal but people have reported flying without any seal at all and having no noticeable performance issues. However, you want to keep ram air out of the lower side of your plenum to keep the differential pressure up for cooling so a seal is necessary.

jimgreen · #6 01-19-2010, 01:45 PM

Thanks for the replies everyone. I guess I can delay worrying about snout seal and ramp seals until I'm flying. I think I'll cut back the cowl inlet a bit more though.